Laser irradiation of semiconductor material surfaces is well known for applications such as thermal annealing of amorphous silicon to obtain re-crystallization, and dopant activation. This technique offers significant advantages over a conventional heating process by enabling a very fast heat treatment and shallow depth of the heated region.
Since the shape and/or size of the laser beam spot usually does not fit to the shape and/or size of the region to be irradiated, the state of the art provides a number of means for shaping the laser such that a region of a semiconductor material layer with particular size and shape or a pattern of such separated regions can be irradiated. For example, a commonly known technique, as illustrated in US2003199176, is using a shadow mask for shaping the laser beam spot. Such shadow mask may have a plurality of apertures.
Since the laser spot size is much smaller than the size of a die (also called a chip or device) due to the high energy density required for the irradiation process and the low output energy of traditionally available laser sources, a first disadvantage of using the conventional shadow mask technique is that, when a whole die or a big pattern within one die has to be irradiated, the laser spot has to step over or scan the die or the pattern to irradiate it completely. This may result in decreased processing speed and increased production cost.
A second disadvantage is that, if the laser spot scans or steps over the pattern, non-uniformities in dopant activation rate or depth and in surface quality may be generated due to fluctuations in laser energy density.
A third disadvantage is that, in case the size of a continuous pattern, i.e. a pattern of non-separated regions, to be irradiated is greater than the laser beam spot, successive laser spots will overlap at some portions of the pattern causing non-uniformities in dopant activation rate or depth and in surface quality.
Considering the drawbacks of the above laser irradiation processes, there is a clear need for the laser irradiation apparatus according to the present invention, which as a first object may provide the ability to process semiconductor material layers without stepping or scanning over a pattern or a die to completely irradiate it, which may results in increased processing speed and decreased production cost.
As a second object the present invention may provide an apparatus of which the process performance is less dependent on fluctuations in laser energy density and as a consequence achieves increased within die uniformities regarding dopant activation rate or depth and in surface quality.
As a third object the present invention may provide an apparatus allowing the user to control and adjust the shape and/or size of the laser beam spot to the geometry of the region to be irradiated, thereby increasing production rate and production flexibility.
As a fourth object the present invention may provide an apparatus allowing reduction or even suppression of overlap and as a consequence increased uniformities regarding dopant activation rate or depth and surface quality.
As a fifth object, the present invention may limit significantly the number of optical elements required for allowing matching shape and/or size of the beam spot to the region to be irradiated, thus reducing the cost and size of the apparatus.
The present invention meets the above objects by using a primary laser beam which is shaped into a plurality of secondary laser beams by a means for shaping comprising a plurality of apertures of which the shape and/or size corresponds to the shape and/or size of a common region of the semiconductor material layer to be irradiated, and by using an optical system adapted for superposing the secondary laser beams to irradiate said common region.